Traditionally, retaining cages are used for restraining the rolling elements (balls, taper rollers or other rolling elements) regularly spaced equidistantly along the raceways of a rolling-contact bearing.
An equidistant arrangement of the rolling elements favours uniform distribution of the contact pressures, and therefore of the overall stresses acting on a bearing, favouring its regular operation, to the advantage of the useful life of the bearing. In general, as the rolling elements get closer together, the specific contact pressure that they exert against the raceways diminishes, and vice versa.
For a constant relative speed of rotation between the outer and inner rings, equal spacing of the rolling elements means that the various rolling elements move at a regular and equal frequency past a given point taken as reference along one of the rings of the bearing. If the frequency of the passing of the various rolling elements comes into resonance with a natural frequency of the bearing or of other bodies to which the bearing is fixed, in certain cases an undesired noise is generated which increases progressively, becoming unacceptable in certain cases.
There is an ever increasing tendency, in certain sectors of the art, towards a reduction in vibrations and better acoustic quality, for example in the domestic electrical appliances sector. To obviate the disadvantage mentioned above, restraining cages have been proposed having pockets with differentiated and irregular angular distribution, in order to obtain better performance from the bearing in terms of smaller vibrations.
There is known from document WO 00/42329 A1 a rolling-contact bearing provided with a retaining cage capable of restraining the rolling elements spaced apart by angular distances which are different from one another.
An intrinsic disadvantage of the solution according to the known art mentioned above, which provides for the introduction of irregularity in the distances between rolling elements, is caused by the fact that precisely these irregularities generate imbalances in the forces and reactions exchanged by the bearing with the components connected to it. In other cases, the irregular distribution gives rise to excessively high peaks in the specific contact pressures, inevitably shortening the useful life of the bearing.
The present invention is therefore tasked with the object of creating a retaining cage of the type specified above in which the aforesaid qualities of quietness and absence of resonance are conserved, eliminating at the same time the negative phenomena associated with imbalances of forces and pressure peaks.